1. Field of the Invention
This application relates generally to methods and devices for replacing an intervertebral disc. More specifically, the application relates to an implantable disc replacement which may be implanted using minimally invasive surgical techniques or percutaneously, and methods for manufacturing such a disc replacement/prosthesis.
2. Description of Related Art
A common medical issue is back pain due to spinal disc injuries caused by trauma, the aging process or other disorders. One method of treatment that has been proposed is to remove the existing nucleus pulposus and replace it with a nuclear prosthesis formed in situ using open surgery or minimally invasive surgical techniques. One proposed method comprises the steps of (i) providing a mold, such as a balloon, to contain a flowable curable material that can cure in situ within the disc space, (ii) providing a conduit to connect the mold cavity to a source of flowable curable material, (iii) delivering the flowable curable material into the mold to fill the cavity, and (iv) permitting the curable material to cure.
The existing techniques for forming a nuclear prosthesis in situ have not achieved convincing clinical acceptance or commercial success. One problem identified by the present inventors is the substantial difference in the modulus of elasticity between the vertebral bony elements, including the vertebral end plates, and the annulus fibrosus on the one hand, and the implanted elements on the other. The high modulus of elasticity of the implanted material is disadvantageous since it does not dampen impacts or sudden increases in intradiscal pressure during extreme bending or torsion, especially during high loading peaks. The large difference in the modulus of elasticity between implanted disc materials and adjacent tissues can also lead to softening of the vertebral end plates and adjacent bone (spongeosus), resulting in subsidence of the nuclear implant. Migration and expulsion of the implant can also occur.
Therefore, there is a need for an improved nuclear implant.